1. Field of the Invention
This invention relates to a camera having a display device for forming a display within a view finder and more particularly a display device for effecting a display that indicates that the camera is in focus.
2. Description of the Prior Art
Heretofore, cameras incorporating a focus detecting device have included a display device for displaying a mark outside the visual field of the view finder which indicates the direction in which a lens should be turned for focusing. The display device of this type, however requires operation of the distance ring of the lens while watching the direction indicating mark. The distance ring cannot be operated while watching a distance measuring target, i.e., an object to be photographed. This presents a great inconvenience. A recently proposed method, called the superimposed display method attempts to eliminate this inconvenience by superimposing a display on an object image within the view finder visual field of the camera. In this display method, a lens-turning direction indicating mark is displayed by superimposing it near a distance measuring target to permit a photographer to focus while simultaneously watching both the object and the indicating mark.
FIGS. 1 and 2 of the accompanying drawings show display devices of conventional methods. The display device of FIG. 1 displays a lens-turning direction indicating mark outside the visual field of the view finder. The illustration shows the view finder's visual field 1; a distance measuring area 2; lens-turning direction indicating marks 103a and 103b; an in-focus mark 103c and a light measurement range 4. Focus detection is performed according to the image of the distance measuring area 2. The distance ring of a photo-taking lens is turned leftward when the lens-turning direction indicating mark 103a lights up and rightward when the mark 103b lights up. The in-focus mark 103c is arranged to light when the lens is in focus. FIG. 2 shows a display device of the superimposed display type. The illustration of FIG. 2 shows a view finder's visual field 1; a distance measuring area 2; lens-turning direction indicating marks 3a and 3b; and a light measuring area range 4. In this device, the lens-turning direction indication mark 3a or 3b lights up to indicate that the distance ring of the phototaking ring is to be turned to the left or to the right; both of these indicating marks light up to indicate an in-focus state.
Normally, a focusing operation should be performed while watching an object image. Hence it is an important feature of a single-lens reflex camera that a focusing operation can be performed while watching the blurred degree of the object image. The FIG. 2 prior art device is superior to the FIG. 1 prior art device in achieving this goal. However, the superimposed display of an in-focus state within the view finder visual field eclipse part of the object image. Such an eclipse not only hinders photographic operation but also presents the following problem: Both the lens-turning direction indicating marks 3a and 3b might be erased in the in-focus condition. Then, since the photographer has been positively informed of an out-of-focus state, the absence of any display of an in-focus condition is undesirable because it may give a photographer a psychologically uneasy feeling. In other words, the photographer might mistake an in-focus state for a malfunction of the focus detecting device, disappearance of the display due to a power supply voltage drop, or a condition in which the focus is not detectable.
Although the prior art arrangement of having a superimposed display of the lens-turning direction indicating mark near the distance measuring part is highly advantageous for focusing, it has been unsatisfactory for effectively displaying an in-focus state.